One common way to connect a pair of optical fibers is to hold their ends in substantial abutment and in precise alignment. Precise alignment can be achieved by providing a sleeve with an accurate internal cylindrical surface that closely receives ferrules attached to the ends of the two fibers, to guide one ferrule in slidable movement along the sleeve until the tips of the fibers substantially abut. U.S. Pat. No. 4,140,367 by Makuch describes a connector system of this type. The alignment sleeve must be accurately formed, as by machining, and is not conducive to manufacture by injection molding of plastic. Another approach, described in U.S. Pat. No. 4,964,690 by Lappohn describes an arrangement where an alignment sleeve that slidably receives ferrules attached to the ends of the two fibers that are to abut, has a middle sleeve portion with slits, with the areas between the slits being compressed inwardly against the two ferrules to align them. The slitted sleeve portion must be of considerable length to enable its inner surface between the slits, to remain substantially cylindrical despite being inwardly bowed to press against the ferrules. The ferrules are biased against one another by springs which require one of the optical fibers to be slidable into and out of the rear end of the ferrule, which prevents fixing the rear end of the ferrule relative to the connector housing.
While prior optical fibers used glass cores which were very thin, such as three thousandth inch in diameter, a more recent approach is to use plastic fibers with a much larger light-transmitting core of a diameter such as one millimeter (about 39 thousandths inch). Such plastic fibers enable the use of low cost connectors with important parts formed by plastic molding injection. However, plastic injection molding generally results in parts of less precision than those obtained by machining of metal. A fiber optic connector system which was relatively compact, which assured accurate alignment of substantially abutting optical fibers despite substantial tolerances in the manufacture of connector parts, and which avoided the need for the rear ends of the optical fibers to slide relative to the connectors, would be of considerable value.